1. Field of the Invention
The present invention relates to an electromagnetic valve to be provided, for example, in a hydraulic control circuit of an automatic transmission of an automobile, FIG. 8 is an illustration of an automatic transmission of the prior art that may be used with the inventive hydraulic valve.
2. Description of the Related Art
Conventionally, an electromagnetic valve has been known in which a spool, which is accommodated in a valve housing so as to be capable of reciprocating, rests at a position where equilibrium is attained between the following forces: the urging force of a coil spring urging the spool toward a linear solenoid, a driving force generated by a current supplied to a coil which causes a plunger to be attracted to an attracting portion to thereby cause a shaft to push the spool, and a force received by the spool from an oil chamber of a feedback chamber (see, for example, JP 2003-139261 A (FIG. 1)).
However, the housing has an input port formed so as to be perpendicular to the axis of the spool, so that working fluid having passed the input port is guided to the interior of the housing of the electromagnetic valve while perpendicularly colliding with the spool; thus, a lateral force due to the collision dynamic pressure of the working fluid acts on the spool, resulting in an increase in the sliding resistance during the operation of the spool and a sealing defect when shutting off the working fluid.
Further, the working fluid is divided, starting from the point at which it collides with the spool, into a plurality of flows along the outer peripheral surface thereof, and these flows join again on the opposite side of the inflow port, thus generating a complicated flow; thus, the working fluid undergoes a marked reduction in velocity and an increase in fluid resistance, resulting in a deterioration in the efficiency with which the working fluid is discharged through a discharge hole; further, foreign matter (contaminant) contained in the working fluid also enters the housing and undergoes a reduction in velocity as the working fluid is decelerated, and is liable to stay around the spool, with the result that foreign matter is caught between the sliding surfaces of the spool and the housing.